1. Field of the Invention
The present invention relates to a system for electro/hydraulically controlling one or more remotely located valves, and more particularly, to a system for controlling one or more well valves in order to optimize testing of hydrocarbon producing formations. The system also provides for monitoring of selected parameters such as pressure, temperature, and valve position.
2. History of the Prior Art
Each underground hydrocarbon producing formation, known as a reservoir, has its own characteristics with respect to permeability, porosity, pressure, temperature, hydrocarbon density and relative mixture of gas, oil and water within the formation. The cost of building and maintaining a large offshore oil and gas production facility can easily exceed $500,000,000 over the life of the facility. Therefore, extensive testing, sometimes for many months, must be conducted of each new reservoir before the commitment to establish an offshore production facility can be justified. Testing of offshore exploratory wells typically requires a sophisticated system of flow control valves at various locations within the well bore, on the ocean floor, and on the drilling vessel. These valves are designed both to control formation fluid flow for optimum test results and for safety during emergency conditions such as a storm forcing the drilling vessel to leave the well site.
Examples of surface and subsurface well testing equipment are shown on pages 5958 and 5959 of the 1980-81 Composite Catalog published by World Oil.
Suitable apparatus to control fluid flow through a subsea wellhead is shown in Taylor U.S. Pat. No. 3,411,576, issued Nov. 19, 1968. Taylor teaches the first use of subsea test trees (SSTT) suspended in the wellhead and associated blowout preventers to control fluid flow during testing of offshore wells. In the Taylor patent multiple valves with their operators are left in the wellhead, and the production string above the wellhead is released when a disconnect is required such as during adverse weather conditions. Later versions of subsea test trees are shown in the patents to Aumann, U.S. Pat. No. 3,955,623 issued May 11, 1976; Young, U.S. Pat. No. 3,967,647 issued July 6, 1976; and Helmus, U.S. Pat. No. 3,870,101 issued Mar. 11, 1975. U.S. Pat. No. 4,234,043 to William M. Roberts and U.S. Pat. No. 4,375,239 to Burchus Q. Barrington et al disclose subsea test trees designed for deep water well sites. U.S. Pat. No. 3,071,188 to G. M. Raulins discloses a latch assembly satisfactory for use with the present invention.
The above referenced patents are incorporated for all purposes within this application.
Under certain circumstances, particularly deep water testing, a significant amount of time may elapse between initiation of a hydraulic control signal onboard the drilling vessel and the response of a remotely located valve to this signal. Various electrical and acoustic actuators have been developed to reduce the elapsed time before a subsea test tree responds to a signal on a drilling vessel. One limitation of such prior art systems is that spurious electrical or acoustic signals may trigger undesired and possibly even dangerous valve operations.
As reservoir testing technology becomes more sophisticated, more is learned about testing procedures and data requirements to accurately evaluate the size of a reservoir. It is clear that a system which provides for reliable and quick operation of various flow control valves will improve the accuracy of well testing. In addition, a system which constantly monitors critical well parameters, system operating limits and valve status adds to the safety of well testing and allows better correlation between measurements of formation fluid flow and equipment changes affecting this flow. Microprocessor technology offers the opportunity to measure many parameters and to rapidly respond to changes in these parameters. It is highly desirable to provide a fully programmable system which can quickly and reliably operate multiple flow control valves remotely located from a central location and measure responses to any change in a valve's status. The present invention provides such full programmable capability to optimize both safety and accuracy of well testing.
The valve control system of the present invention is not limited to controlling multiple remotely located valves during well testing. The system can be modified to control remotely located valves during long term production from an oil and gas well or any other system of remotely located valves or hydraulic equipment. The present invention is described for use in a well testing system which has a retainer valve with a locking mechanism, a subsea test tree, and an emergency disconnect latch assembly.